In forming a tire, there is used a mold which applies a pressure to the inside of a formed green tire and brings the outer surface of the green tire into pressure contact with the inner wall of the heated mold to vulcanize the green tire with heat and under pressure. On the internal surface side of such a mold (on a tread side of the tire), a plurality of narrow belt-like protrusions and blades are provided for forming a tread pattern on the tire. Usually, the mold is divided into a plural number (for example, eight segments) in the circumferential direction.
In the prior art, for example, Patent Document 1 describes one which is designed to decrease the tire noise by being partitioned into predetermined lengths in the circumferential direction of a tire and arranging tread pattern units of plural kinds randomly in the circumferential direction. In the one described in such Patent Document 1, the tread pattern units of the plural kinds which differ in circumferential length are arranged randomly in the circumferential direction to form the tire tread.